Be sure to copy exact folder structure when generating final images

'COPY *' has a different behavior than 'COPY .' - when regexes are
involved, COPY behave differently, by unpacking directory content to the
root.

Enhance unit test to cover the scenario as well

pkg/compiler/artifact.go

@@ -248,7 +248,7 @@ func (a *PackageArtifact) SetPath(p string) {
 func (a *PackageArtifact) genDockerfile() string {
 	return `
 FROM scratch
-COPY * /`
+COPY . /`
 }
 
 // CreateArtifactForFile creates a new artifact from the given file